The present invention relates to an improved auto-steering system, and more particularly relates to improvements in the responsiveness of an auto-steering system having starboard and port motor drivers for rudders of small boats and cruisers.
The navigation mode of a boat is greatly influenced by environmental factors such as navigation course, wind heading and direction of tideway. An auto-steering system is in general accompanied by a sensor circuit including finders adapted for detecting changes, i.e. deviations from the standards, in the above-described factors, and generative of deviation signals corresponding to such changes. The signals are passed to a feedback control circuit in order to cause corresponding rotation of a rudder driver motor, thereby turning the rudder in such a fashion as to compensate for the above-described deviations. Taking the navigation course for example, the deviation signal is generated when the change in the navigation course is purposely carried out and when the change results from any unexpected causes. The present invention concerns processing of the deviation signals in the latter case, i.e. unexpected deviation of the actual sailing course of a boat from the prescribed, i.e. intended, navigation course.
Under the normal condition of sailing, it is preferred that the control accuracy of the system is high enough to cause reactive control operation when the above-described unexpected deviation occurs, i.e. the system is very keenly responsive to the unexpected deviations. However, under abnormal conditions in which waves are very heavy due to storm and/or strong tideway often encountered during motion straight ahead, there is a case in which the boat macroscopically sails on the prescribed navigation course but microscopically often deviates from the prescribed navigation course. In other words, although the boat wholly follows the prescribed navigation course, it often and momentarily sails towards starboard side and port side alternately off the prescribed navigation course. When the control accuracy is too high under this condition, the system responds quite keenly even to very small deviations, thereby causing a great deal of loss in the power consumption and malfunction of relay contacts and the rudder driver motor. This is quite disadvantageous in the case of relatively small boats and cruisers on which charging of batteries is quite difficult or almost impossible to practice.
The above-described small, frequent and alternate deviations of the actual sailing course of a boat from the prescribed, i.e. intended, navigation course under the abnormal environmental conditions are called "chattering deviations".